Telephone system



y 14, 1942- R. TAYLOR ETAL V 2,289,528

TELEPHONE sYsT M Filed April 15, 1940 s Sheets-Sheet 1 F INVENTORS REGINALD TAYLOR 550m? THOMAS BAKER A TTORNE Y July 14, 1942. R, TAYLQR AL 2,289,528

TELEPHONE SYSTEM Filed April 15, 1940 3 Sheets-Sheet 2 N] O I I H bl LP 5m on H c Q; Ca k a INVENTORS REG/NALD TAYLOR GEORGE THOMAS BAKER A TTOPNE Y July 14, 1942. R. TAYLC ET AL 2,

TELEPHONE SYSTEM Filed A ri'l 15, 1940 s Shee ts-Sheet 5 F1 .4. J a g /NVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER ATTORNEY Patented July 14, 1942 UNITED STATES 2,289,528 PATENT ()FFIC TELEPHONE SYSTEM Reginald Taylor and George Thomas Baker, Liverpool, England, assignors to Associated Telephone 8; Telegraph Company, Chicago, 111., .a corporation of Delaware Application April 15, 1940, Serial No. 329,699 In Great Britain May 19, 1939 transmission of the said digit as soon as a switch Claims.

When laying out multi-exchange areas in which it is not proposed to employ register ftranslators, it is found in certain cases that the most economical numbering scheme, that is, one involving the dialling of a minimum number of digits, carries with it the undesirable feature of having to use multiple groups of junctions between exchanges each group having a different numerical significance. This will bethe case 'for instance where the numbering scheme is such that subscribersnumbers on different exchanges commence with the same digit or digits. Under such ascheme the junctions obviously cannot be.

operated at-maximum efliciency sincefor any particular call access can only be had to .one g p of junctions out of a number of such groups extending to a given exchange. It is the general object of the present invention to provide arrangements whereby greater flexibility in the numbering and layout of .non-register-translator areas is obtained together with a more economical and eliicient use of the inter-exchange junctions.

According to one feature of the invention, in a multi-exchange telephone system a register device provided at an originating exchange is arranged to store one or more trains of impulses and delay the transmission-of the said trains of impulses to another exchange until the operation of a discriminator in response to one or more of said trains of impulses has selected the required exchange.

According to another feature of the invention, in a multi-excha-nge telephone system including a plurality of exchanges which are reached from a further exchange in response to the same initial digit or digits, the use of a single group of junctions to any exchange of the plurality is rendered possible by the provision of a discriminator in the originating exchange which responds to the digit following the final common digit and controls the selection of the required exchange while the said digit isthen transmitted to the selected exchange to effect the appropriate selection thereat.

A further feature of the invention is that in a multi-exchange telephone system including a plurality of exchanges which are reached from a further exchange in response to the same initial digit or digits, all such exchanges are accessible by Way of a relay group including -a register device and a discriminating device which are both operated by the digit following the final common digit, the discriminating device serving to route the connection to the wanted exchange and the register device serving to control the rein the wanted exchange is ready to receive it.

According to another feature of the invention, in a multi-exchange telephone system including a plurality of exchanges which are reached from a further exchange in response to the sameinitial digit or digits, the digit following the final common'digit serves to operate a register device and also a discriminating device which determines the required exchange and initiates the hunting operation of a switch to seize a free junction thereto whereupon the register device controls the transmission of the said digit and subsequent digits thereover.

The invention will be better understood from the following description of one method of carrying it into effect, taken in conjunction with the accompanying drawings comprising Figs. 1-4.

Figs. 1 and 2 depict typical trunking layouts of an exchange .A and two other exchanges B and C of an area, the method generally employed in handling outgoing calls from exchange A being shown inFig. 1, while Fig. 2 shows an improved method according to the invention. Figs. 3 and 4 when arranged side by side show circuits of a discriminating relay set suitable for use in the improved scheme of Fig. 2.

The exchanges in the area shown are assumed to be of the well-known decimal step-by-step type,.and it is further assumed that exchange B i is :of 4,000 linesfcapacity and has numbers 56000- 59999 allocated thereto, while exchange '0 is of A 3,000 lines capacity and has allocated to it the numbers 51000-53999.

Referring now to Fig. 1, when the subscriber S removes his receiver he will be connected over his uni-selector U/S to a first selector ISR. In case the wanted subscriber is on either of the exchanges B or C, the first digit dialled will be 5 in response to which the first selector will be raised to the corresponding level to gain access to the 5 group of second selectors. For calls to exchange B the digit 6, 7, 8 or 9 will now be dialled as a second digit, and the second selector will hunt for an idle junction in the selectedgroup of junctions out of the four :groups shown. Assuming that 6 is dialled as a second digit, the connection will be routed over an outgoing autoto-eauto impulse repeater diagrammatically indicated by AR to a 56 group third selector at exchange .13. The third digit will then be received on this switch .and the remaining two digits will be received on a final selector in the required group to route the call to the Wanted party.

If the wanted party is on exchange C, .the digit 1, 2 or "3 will be dialled as a second digit in response to which the call will be routed to one of the third selectors in the relevant group at exchange -C.

With the above arrangements, four groups of junctions are required to exchange B and three groups to exchange C. One way to avoid these multiple groups of junctions would be to increase the number of digits to be dialled but this would be unsatisfactory for the subscriber and also more numerical switches would be required.

The proposed method overcomes these difficulties by replacing the auto-to-auto repeater AR by a discriminating relay set having access to a common group of junctions over a hunting switch and employing an impulse storage and regenerating device preferably of the electromechanical type described in the application of McClew and Woodland, Serial No. 79,830, filed May 15, 1936, now U. S. Patent 2,188,461, of January 30, 1940. The regenerator serves to store the latter part of the called number during the time the hunting switch is searching for a free junction in the common group of junctions extending to the desired exchange.

Considering the operation, the subscriber on dialling the first digit 5 of the wanted partys number will raise the first selector wipers to level 5 in response to which a free discriminating relay set DRS will be taken into use. In the present example subscribers numbers on the two other exchanges B and C are assumed to commence with the same digit 5, and the relay set DRS will be provided with a uni-selector JH, the first set of wipers of which are arranged to.connected with a common group of junctions to exchange B, while the second set connect with a common group of junctions to exchange C.

If the second digit dialled is 1, 2 or 3, these digits will be effective for instance on a counting chain of relays in the relay set DRS or on the switch JH itself to cause the switch to perform a hunting operation with its second set of wipers effective, and as a result a 5 group second selector at exchange C will be taken into use. The discriminating digit and also the subsequent digits received in the relay set are also stored on the regenerator, and when the hunting switch JI-I finds a free junction to the desired exchange C, the first digit 1, 2 or 3 received, followed by the remainder of the digits of the number, will be retransmitted to set up the connection at exchange C.

If the second digit dialled is any one of the digits 6, '7, 8 or 9, thus characterising a call to exchange B, the hunting switch JH will be set into operation with its first set of wipers effective while this and subsequent digits will be stored on the regenerator. When a free junction is found, a 5 group second selector is taken into use at exchange B and the regenerator thereupon sends out the digits stored therein to set up the call at exchange B.

Consideration will now be given to the circuits of a typical discriminating relay set DRS, reference being had to Figs. 3 and 4. This relay set employs an impulse regenerator of the type already mentioned and it also employs a hunting switch of the well-known 25-point electromagnetically-operated reverse drive type. The banks and wipers of this switch are assumed to be divided into two sets associated respectively with two common groups of junctions to exchanges such as B and C of Fig. 2, and the determination as to which of these two sets of wipers and banks is to be used is under the control of relay KB. The hunting switch is arranged to act as a discriminator and respond to the first digit transmitted to the relay set, in this case the second digit of the number dialled. Thereupon in accordance with the position to which it is set it operates either relay HA or HB so as to connect up the set of wipers and banks associated with the exchange representative of this digit. At the end of the train of impulses corresponding to this digit, the switch restores to its normal position and thereafter proceeds to hunt for a. free junction in the common group of junctions extending to the desired exchange.

Facilities are also provided whereby if the second digit of the dialled number is unused, a suitable warning tone is returned to the calling partly.

Considering now the circuit operation with reference to Figs. 3 and 4, when the calling party dials the first digit 5 of a number associated with either of the exchanges B or C, the first selector ISR is raised to the fifth level and seizes a discriminating relay set such as the one shown. A loop is thereupon extended forward over the incoming negative and positive conductors to operate relay A in series with the ballast resistance lamp BRA, and this relay on operating brings up relay B which looks over its armature bl. Relay BA is thereupon operated over armature 112, while guarding earth is applied to the private load P over armature b3. Relay BA prepares an impulsing circuit for the receiving magnet RM of the impulse regenerator at armature bal, pre-' pares an operating circuit for relay C at armature 22112, and at armature bal prepares an impulsing circuit for the driving magnet JHM of the discriminating and hunting switch JH.

If the wanted subscriber is on exchange C, the second digit dialled will be 1, 2 or 3 and relay A in responding thereto will on each release complete an energising circuit at armature a2 for the hunting switch magnet J HM and at armature al for the regenerator receiving magnet RM so that assuming the digit 2 is dialled, the hunting switch wipers will be advanced to position 3 and the digit 2 will be stored in the impulse regenerator.

During the impulse train relay B is intermittently short-circuited by armature al but it remains operated due to the slugging effect of the short-circuiting. The presence of the metal rectifier MRD in the energising circuit of relay B prevents the slowing-up of the magnet operation which would otherwise result from the direct connection of a comparatively low value noninductive resistance YA in parallel with its winding. The short-circuit is removed from the winding of relay C on the first release of relay A and it operates and subsequently holds during the impulse train. At its armature cl it brings up relay P, while at armature 03 the so-called regenerator marking magnet MM is energised.

As regards the impulse storing and regenerating device which is indicated diagrammatically in the circuit by discs R, P and S, it will be understood from the details given in the above mentioned specification that the receiving disc R is rotated step-by-step in response to the impulses When the magnet RM responds to the first digit and commencesto rotate the disc R step-bystep, the first movement of. this disc brings about the mechanical operation of the off normal springs NI whereby an operating circuit is prepared for relay ON. At the end of the train of impulses, relay A remains steadily operated and on the release of relay C after its slow .period, the circuit for the marking magnet MM is opened and this magnet restores, thereby causing the lever carried by the disc R to release and to push a pin corresponding to the digit dialled into the path of the disc S. At the same time the contacts mm controlled by the marking magnet close after having been open during the energisation of the magnet, and complete the circuit for relay ON which thereupon operates and locks for the remainder of the setting operation over its armature on2 and oiT-normal contacts NI to earth. Relay ON also at armatures 0115 and on6 prepares the connection of the regenerator impulsing springs IMP to the outgoing side of the relay set, and further prepares the circuit to the sending magnet SM at armature 0713.

The hunting switch J H also will have been set to position 3 in response to the train of impulses and on the release of relay C at the end of the train, a circuit is completed form earth over armatures bail, ha l and c2 and wiper JH8 in positioni to bring up relay I-IB. This relay at its armature hbl brings up relay HA, and at armatures M12, M73 and M24 connects up the lower set of wipers and banks JHZ, JH4 and JHB which connect with a group of junctions extending to exchange C. From the strapping on the bank JH8 it will be seen that if any one of the digits 1, 2 or 3 is dialled as the second digit of the number, relay HB willbe operated to connect up the lower set of wipers, while if any one of the digits 6, 7, 8 or '9 is dialled, relay HA only will be operated and the upper set of wipers which connect with a common group of junctions extending to exchange B will be used. The strapping connections to the JH8 bank may be altered to suit any numbering arrangement.

Continuing the consideration of the call in which digit 2 is dialled, relay HA locks up over armature had and holds relay H-B over the same circuit. At armature hal it disconnects any further impulsing circuit to the magnet JHM, at armature haZ prepares a circuit for returning busy tone to the calling party if all junctions in the required group are engaged, and at armature hat completes a homing circuit for the switch JH from earth via bank and wiper JH 'I, armatures M13 and y'hr3, magnet interrupter contacts :ihm, magnet J HM to'battery. The wipers of the switch are thereupon restored to the home position 1, whereupon the short-circuiting earth previously applied over bank and wiper JH'I to relay JHR is removed and this relay now operates in series with the magnet, it beingunderstood that the resistance of relay JHR is such that the magnet will neither operate nor hold in series therewith. Relay J HR looks over its make-first light armature yhrl and at armatures jhrZ and y'hr3 connects relay K and the magnet JHM to the lower testing wiper J H6, whereupon the switch JH commences to hunt in search of a free junction in the selected common group.

If the junction connected to contact I in the lower banks is engaged, the test wiper JHB will encounter earth which short-circuits relay K and is extended via the interrupter contacts a'hm to energise the magnet JHM. Magnet JHM opens its own circuit at contacts ihm and thereupon advances the wipers to position 2. The selfinterrupted driving operation of the switch JH continues until a free junction in the group is found, whereupon wiper JHG fails to encounter earth, and since relay K is no longer shortcircui'ted, it operates in series with the magnet JHM which is non-operative in series with relay K. Relay K at armature kl applies earth via armature hbfi and wiper and 'bank JHG to guard the junction seized, and at armatures k3 and k4 connects the regenerator impulsing springs IMP through to wipers JHZ and JH4 and hence to the seized junction extending to exchange C.

Meanwhile the third and subsequent digits of the calling number may have been received at the relay set and if so they will have been mechanically stored on the regenerator device.

Re-transmission of the stored digits cannot take place until relay K operates and when it does so a circuit is completed over armatures 705, 0123, p! and ipl to e'nergise the sending magnet SM. Thereupon't'he pin displaced at the end of the previous call is pushed out of the path of the disc S, but owing to the stepped head on the reset pm, this disc is not immediately released, and remains held until the magnet SM is de-energised. Magnet SM at its contacts sm disconnects relay P which thereupon opens the magnet energising circuit at armature pl and, as fully described in the prior specification, the sending disc S is now released and rotates until it comes up against the stop pin indicating the termination of the first train of impulses. During the rotation of the disc S, the pulses of the first train received are sent out in regenerated form by way of the impulsing springs IMP controlled from the regenerator device, and these impulses serve to set the selector in the distant exchange C; Relay -P on releasing re-energises the sloW- to-release relay IP in preparation for timing the inter-digital pause after the sending out of the train of impulses.

During this time if further trains of impulses are received on the receiving disc, the two operations of reception and re-transmission may 'go on simultaneously but independently of each other.

When the disc S comes up against the stop pin indicating the termination of the first train of impulses, relay P is again operated in a circuit including the pins and relay IP is disconnected. After the release time of relay IP which determines the inter-digital pause, the sending magnet SM again receives a momentary energisation in transmitted, the sending disc S will catch up with the receiving disc R whereupon the off-normal contacts NI open and release relay ON in order to re-connect the incoming and outgoing sides of the relay set line circuit, while relay P is finally released. v

When the called party replies, the battery is reversed in well-known manner on the called side of the circuit, whereupon rectifier MRB shunting relay D now becomes non-conductive and rectifier MRA conductive so that this relay operates. Thereupon it brings up relay DD which at armatures ddl and ddZ reverses the current flow over the incoming conductors for supervision purposes, and at armature dd}! connects earth by way of the right-hand winding of relay DA to the S pulse lead extending to a meter pulse machine which it will be understood is arranged to supply battery pulses to the S and Z leads with a definite time relation.

On the transmission of the next S pulse, relay DA is operated and at armature dal prepares a circuit for relay DB which is operated after the appropriate time interval from the Z pulse in series with the middle winding of relay DA. Relay DA remains locked over its left-hand winding until relay DB operates from the Z pulse, when both the initial energising circuit and the locking circuit for relay DA are opened but it remains held over its middle winding in series with the left-hand winding of relay DB for the duration of the Z pulse.

During the application of this latter pulse, relay MP is connected by way of armatures da3, db! and M15 to one or other of the meter pulse leads II and i2, and relay MP will thereupon be operated one or more times in accordance with the meter fee for the particular junction group selected. At armature mpl positive battery is connected up to the incoming P conductor so as to actuate the subscribers meter the appropriate number of times. 'At the end of the Z pulse, relay DA restores to prevent any further operation of the metering relay MP and relay DB remains operated over its right-hand winding to earth via armatures dbl and ba l.

At the end of conversation if the called party hangs up first, relays D and DD will release so that earth is extended over armatures dd l and 03114 to light the supervisory lamp LP in series with delayed alarm equipment connected to common lead l0, an alarm being initiated if the calling subscriber now fails to hang up after a predetermined time.

When the calling party hangs up, relays A, B and BA release in turn, whereupon relays JHR, K, HB and other relays held operated therefrom are released and a homing circuit is completed for the switch JI-I from the earthed bank JI-II.

In case the calling party should release the connection prematurely, i. e., during the setting up of the call, when relay B releases, the guard earth is removed from the P lead for the release time of relay BA during which time any equipment preceding the relay set is allowed to release. On the release of relay BA the private lead remains guarded over armatures p3 and 01M until such time as all the digits stored in the regenerator have been sent out, this operation being initiated at armature ba3. It will be noted that the circuit from the impulsing springs IMP is disconnected at armature b4 so that the sending out of impulses from the regenerator is rendered ineffective in this instance.

If the second digit dialled by the subscriber, i. e., the first digit received at the relay set, represents an unallocated number, a circuit completed over contacts on the bank Jl-IB corresponding thereto serves to operate relay NB. This relay on operating in response to the dialling of such a digit connects number unobtainable tone via lead [3 to the right-hand winding of the retard I and this tone is thereupon induced in the left-hand winding, and finds its way on to the line conductors so as to inform the subscriber that he has dialled incorrectly.

In case all the junctions in the selected common group are engaged, the switch JH will rotate to the last position whereupon relay K operates and completes a circuit from its earthed armature kl to operate relay NB. Although at armatures R3 and led a connection is extended to the wipers y'hl and 9h3 or 571.2 and 771.4, as the case may be, this connection is ineffective in this condition as the contacts 25 on these banks are not wired. Relay NE in this case returns busy tone to the calling party owing to the operation of relay HA, the circuit being completed from the earthed busy tone source connected to lead I, armature ha2, armature M32 and the righthand winding of retard I to earth whence the tone is extended by induction to the line conductors.

Considering the function of rectifier MRC, this serves to maintain a guard earth on the P lead during the transit time of armature mp! and at the same time prevents the booster battery from being short-circuited by the earthed armature 193 when connected up to the private. As regards resistance YB, this serves to maintain a reduced holding current through the winding of the impulsing relay at the distant exchange during the transit time of relay ON and so prevents the relay from releasing during changeover conditions.

Although in the circuit described the switch JH is assumed to be of the 25-point type it could be replaced in the case of larger junction groups by two switches each having wipers out of phase so as to provide in well-known manner a capacity of 50 points.

Furthermore it will be appreciated that the invention is not limited to the particular example described and that it may be applied to exchange areas in which subscribers numbers at more than two exchanges commence with the same digit, the only modification required being that further switching relays HC, HD, would be required. The invention can also be utilised in cases where more than one of the initial digits are the same for subscribers on different exchanges. It will be understood also that in some circumstances it might be more convenient to make use of a discriminator separate from the hunting switch.

From the foregoing description it will be seen that the invention provides a very ready means of avoiding the use of ineflicient and uneconomic junction groups, while the use of regenerators in the carrying out thereof also assists in improving the dialling range throughout the area.

We claim:

1. In a switching system, an automatic switch having access to different groups of trunks, means for seizing said switch and transmitting any one of certain digits thereto, means for operating said switch first to register said digit and then reoperating said switch to search for an idle trunk in a group depending upon the digit registered, other means associated with said switch also operated to register said digit, and means always controlled by said last means after said switch has found an idle trunk to transmit over said trunk impulses depending upon the digit registered by said last means.

2. In a switching system, an automatic switch having access to two groups of trunk lines, means for seizing said switch and transmitting a digit thereto, means for operating said switch first to register said digit, means controlled by said registration for then operating said switch to search for an idle trunk line in one of said groups if the registered digit has any of certain predetermined values or to search for an idle trunk line in the other of said groups if the registered digit has any of certain other predetermined values, other means associated with said switch also operated,

to register said digit, and means always controlled by said last means after said switch has found an idle trunk line in either of said groups to transmit over that trunk line impulses depending upon the digit registered by said last means.

3. In a switching system, an automatic switch whose wipers have access to two groups of trunk lines, means for seizing said switch at different times and transmitting different digits thereto, means responsive to said digits for operating said switch at each of said times to register the digit transmitted to said switch, means then operated over a wiper of said switch to characterize one of said groups of trunk lines, the group characterized depending upon the digit registered by said switch, means controlled by said last means for reoperating said switch to seize an idle trunk line in the characterized group, and means effective after said trunk line has been seized to automatically transmit over that trunk line the same digit registered by said switch.

4. In a telephone or like system, a local exchange having inter-exchange trunk lines extending to each of a plurality of distant exchanges, a switch in the local exchange having access to said trunk lines, means for transmitting the telephone number of a wanted subscribers line, means effective only if one or more of the initial digits of said number comprise a predetermined digitial code to operate said switch to register the digit following said one or more initial digits, means controlled over said switch by the digit registered for characterizing a particular one of said distant exchanges depending upon the digit registered, means for then reoperating said switch to search for an idle trunk line to the characterized distant exchange, and means effective after said trunk line has been found to always transmit over that trunk line the same digit registered by said switch.

5. In a telephone or like system, a local exchange having inter-exchange trunk lines extending to each of a plurality of distant exichanges, a switch in the local exchange having access to said trunk lines, means for transmitting the telephone number of a wanted subscribers line, means effective only if one or more of the initial digits of said number comprise a predetermined digitial code to operate said switch to register the digit following said one or more initial digits, means controlled over said switch by the digit registered for characterizing a particular one of said distant exchanges, depending upon the digit registered, means for then. reoperating said switch to search for an idle trunk line to the characterized distant exchange, other means associated with said switch also operated to register the same digit as registered by said switch, and means controlled by said last means after said switch has found an idle trunk line to transmit over said trunk line impulses depending upon the digit registered by said last means.

6. In a switching system, an automatic switch whose wipers have access to two groups of trunk lines, mean for seizing said switch and transmitting impulses thereto, means responsive to said impulses for operating said switch step-by-step in accordance with said impulses, means then controlled variably over a wiper of said switch to characterize one of said groups of trunk lines,

the group characterized depending upon the position occupied by said wiper after said impulses have been received, means controlled by said last means for reoperating said switch to seize an idle trunk line in the characterized group, and means effective after said trunk line has been seized to automatically transmit over that trunk line impulses corresponding to said impulses transmitted to said switch.

7. In a switching system, an automatic switch whose Wipers have access to two groups of trunk lines, means for seizing said switch and transmitting impulses thereto, means responsive to said impulses for operating said switch step-bystep to register said impulses, a device associated with said switch also operated to register said impulses, means then controlled variably over a wiper of said switch to characterize one of said groups of trunk lines, the group characterized depending upon the position occupied by said wiper after said impulses have been registered by said switch, means controlled by said last means for reoperating aid switch to seize an idle trunk line in the characterized group, and means controlled by said device after said trunk line has been seized to transmit over said trunk line impulses corresponding to those registered by said device.

8. A system as claimed in claim 7, wherein said device comprises a mechanical impulse repeater.

9. In a switching system, an automatic switch whose wipers have access to two groups of trunk lines, said wipers occupying a normal position, means for seizing said switch and transmitting a train of impulses thereto, means responsive to said impulses for operating said switch away from normal a number of steps depending upon the number of impulses in said train, means then controlled variably over a wiper of said switch to characterize one of said groups of trunk lines, the group characterized depending upon the position occupied by said wiper after said impulses have been received, means controlled by said last means for restoring said switch to normal and then reoperating it to search for and seize an idle trunk line in the characterized groups, and means effective after said trunk line has been seized to automatically transmit over that trunk line a train of impulses corresponding to said train of impulses transmitted to said switch.

10. In a switching system, an automatic switch having two groups of wipers and an additional special wiper, certain trunk lines accessible only to one group of wipers, other trunk lines accessible only to the other group of wipers, means for seizing said switch and transmitting impulses thereto, means responsive to said impulses for operating said switch step-by-step in accordance with said impulses, means controlled variably over said special wiper in accordance with the position occupied by that wiper after said impulses have been received for rendering only a single one of said groups of wipers effective and for reoperating said switch to search for and seize an idle trunk line with that group of wipers, and means effective after said trunk line has been seized to transmit over that trunk line impulses corresponding to said impulses transmitted to said switch.

REGINALD TAYLOR.

GEORGE THOMAS BAKER. 

